Twelve people have been killed and 58 wounded after a masked gunman shot moviegoers at the latest 'Batman' premiere in Colorado. The attack is the worst in the state's history since the infamous Columbine High School massacre in 1999.

­Thirty people remain in hospitals, 11 of whom are believed to be in critical condition, Gov. John Hickenlooper said.

How it happened

The theater in the Colorado city of Aurora in the Denver Metro area was packed with a lot of people, many of them young fans, at the time the shooting started, 9news reports. The violence erupted some 15 minutes after the movie began, witnesses said.

Many moviegoers had dressed up to attend the premiere of the latest Batman film. The gunman, who would have stood out in other circumstances, may have managed not to attract attention before he launched his attack.

Police say that the assailant approached the theatre from the back, and initially opened a chemical gas canister. Witnesses recounted hearing a hissing sound and smoke.

The shooting started while a gunfight was underway onscreen. Some people said that when they first heard the gunfire, they thought it was some kind of promotional trick or a special effect.

Witnesses reported seeing a tall, gun-wielding man clad in body armor and wearing a gas mask in the theatre. The assailant attempted to block the exits to trap the moviegoers inside. Some said the gunman managed to empty at least two clips.

One of the injured moviegoers posted a picture of his "near brush with death" online.

The young man was treated for a gunshot wound in a Colorado hospital. Image taken and posted online by http://themurderator.imgur.com/

At least 12 dead, including children

Twelve people died in the horrific attack, and the youngest victim is believed to be just 12 years old.

In a tragic twist of fate, one of the victims of this rampage was aspiring sportscaster Jessica Ghawi – who survived the Eaton Centre shooting in Toronto just one month ago. In a moving blog post she wrote a few weeks ago, Jessica spoke about that day, saying she " saw the terror on bystanders’ faces."

"I saw the victims of a senseless crime. I saw lives change. I was reminded that we don’t know when or where our time on Earth will end. When or where we will breathe our last breath," the journalist wrote.

Her brother Jordan confirmed her death to reporters as he was catching a flight from her native San Antonio, Texas to Denver.

He took to Twitter to say "'This could easily be the worst night of my life. It appears that my sister has been fatally wounded in a mass shooting at a movie premiere in Denver, CO."

Jessica was attending the premiere with a friend, Brent Lowak, who was reportedly shot at least one time and was taken to a nearby hospital.

Fifty-eight others were admitted to six local hospitals, many in critical condition.

An area children’s hospital said the youngest of the six shooting victims brought to them is six years old. Not all of the patients at the hospital are children, however.

Another local hospital is treating a baby as young as three months old who was wounded in the shooting. Some witnesses to the shooting said they saw a baby who had been injured in the theater. The baby's condition is unknown at this time.

Several victims are being treated for chemical exposure rather than gunshot wounds, medical staff say.

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The aftermath

The FBI is considering raising the national security level nationwide following the shooting, Sky News says citing its sources.

The Paris premiere of 'The Dark Knight Rises' has already canceled due to tragic events in Colorado. The New York Police Department has also said it will be providing security at all the theatres screening the latest Batman movie across the five boroughs.

President Obama has addressed the nation, after cancelling a campaign event in Florida.

"This morning, we woke up to news of a tragedy that reminds us of all the ways we are united as one American family. … We're still gathering all the facts about what happened in Aurora but what we do know is the police have one suspect in custody. And the federal government stands ready to do whatever is necessary to bring whoever is responsible for the heinous crime to justice," the President said.

Obama also ordered US flags be flown at half-staff until July 25 as 'mark of respect' for shooting victims in Colorado.

Christopher Nolan, the director of Dark Knight Rises, has called the massacre a senseless tragedy. “Nothing any of us can say could ever adequately express our feelings for the innocent victims of this appalling crime, but our thoughts are with them and their families,” he said in a statement.

In the wake of the tragedy, Warner Brothers pulled a promotional trailer for upcoming film "Gangster Squad," which was playing before showings of "The Dark Knight Rises," from theaters.

Mobster movie "Gangster Squad," set in the 1940s and 1950s, chronicles the Los Angeles Police Department's fight to keep the mafia out of its city. The film features a scene in which men open fire with machine guns on an audience in a movie theater.

The studio had even considered cancelling screenings of the latest Batman flick, and many TV channels, including NBC, CBS and ESPN, have pulled 'Dark Knight Rises' ads off air.

In the wake of the Colorado tragedy, AMC Theatres have also banned moviegoers from attending the screenings in costume.